Remove old custom Identifiable type

Pachyderm/Model/Notification.swift

@@ -38,3 +38,5 @@ extension Notification {
         case follow
     }
 }
+
+extension Notification: Identifiable {}

Pachyderm/Model/Status.swift

@@ -129,3 +129,5 @@ extension Status {
         case direct
     }
 }
+
+extension Status: Identifiable {}

Pachyderm/TimelineSegment.swift

@@ -8,7 +8,7 @@
 
 import Foundation
 
-public struct TimelineSegment<Type: Identifiable> {
+public struct TimelineSegment<Type: Identifiable> where Type.ID == String {
     private var ids: [String]
     
     public init(objects: [Type]) {
@@ -47,11 +47,3 @@ extension TimelineSegment: RandomAccessCollection {
         return ids.endIndex
     }
 }
-
-// todo: remove me when i update to beta 5, Identifiable is now part of Swift stdlib
-public protocol Identifiable {
-    var id: String { get }
-}
-
-extension Status: Identifiable {}
-extension Notification: Identifiable {}